In recent years, techniques for detecting linear marks have been disclosed. The linear mark here means, as shown in FIG. 7, for example, a mark of a width of a white line or the like which is a kind of a lane line drawn on a road surface. PTL 1 discloses a technique related to a linear mark detector for detecting a white line in a road image.
FIG. 11 shows a configuration of a system including the linear mark detector disclosed in PTL 1. This system includes a road image input apparatus 910, a white-line image width determining unit 901, a white-line inside/outside luminance difference computing unit 902, a white-line end edge intensity computing unit 903, a white-line internal luminance uniformity computing unit 904, a white-line feature integrating unit 905, and a white-line feature point data output unit 906. An operation of the system will be described below.
The road image input unit 910 inputs a road image. The white-line image width determining unit 901 determines a width of an image at each point on a road image based on its ordinate in the case where a white-line image exists on the point. The white-line inside/outside luminance difference computing unit 902 computes a difference in luminance value between the inside and the outside of a white-line region based on a position and a width of the white-line image, the width being determined at each point on the road image by the white-line image width determining unit 901. The white-line end edge intensity computing means 903 computes edge intensity at an end of a white line based on a width of the white-line image, the width being determined at each point on the road image by the white-line image width determining unit 901.
The white-line internal luminance uniformity computing unit 904 computes uniformity of luminance in a white line based on a width of the white-line image, the width being determined at each point on the road image by the white-line image width determining unit 901. The white-line feature integrating unit 905 integrates feature values computed by the white-line inside/outside luminance difference computing unit 902, the white-line end edge intensity computing means 903, and the white-line internal luminance uniformity computing means 904 to give an evaluation value indicative of a likelihood of a white-line feature point to each point in the road image. The white-line feature point data output unit 906 outputs the evaluation value.